1. Field of the Invention
This invention relates to a control device in a continuously variable transmission system (hereinafter referred to briefly as "CVT") used as a power transmission system in a vehicle, and more particularly to control during transient time of the vehicle.
2. Description of the Prior Art
The CVT is provided on a power transmission route of an engine and a speed ratio e (=Nout/Nin, where Nout and Nin are rotational speeds on the output and input sides of the CVT) thereof is controlled such that an engine rotational speed can be a target engine rotational speed. For example, in Japanese patent application No. 67362/1982 filed by the present applicant, the target engine rotational speed is set at an engine rotational speed for achieving a required output of the engine, which is commensurate to an intake throttle opening during the steady time at the minimum fuel consumption rate regardless of the steady time or the transient time of the vehicle. In consequence, a satisfactory driveability is not obtained during acceleration and deceleration and, during running where accelerations and decelerations are alternatley repeated, the target engine rotational speed is considerably varied, whereby a time period required for the shifting of the CVT is lengthened, and an efficiency of the power transmission, namely the fuel consumption rate is deteriorated.
To obviate this, it is conceivable that in addition to D (Drive) range, a 2nd range where a target engine rotational speed during acceleration and deceleration is set separately the case of D range, and a driver manually shifts to the 2nd range during acceleration and deceleration. However, this presents such a disadvantage as to make the operation complicated.
Japanese Patent Laid-Open No. 180864/1983 teaches that an acceleration of the vehicle is detected, and, when the acceleration is small in value, a transmission ratio (a transmission ratio is an inverse number of a speed ratio e) of the CVT is increased. However, the transmission ratio during deceleration can not be distinguished from the steady time in particular, whereby, during running where accelerations and decelerations are frequently repeated, a satisfactorily good driveability has not heretofore been obtained.